1. Field of Invention
The invention relates to a structure of a converter for correcting the resonance frequency between the backlit panel assembly of a liquid crystal display and an transformer of an AC inverter, which corrects the parasitic capacitor to increase the whole efficiency of the AC inverter under the premise of not changing the transformer of the AC inverter, and, more particularly, to a converter which has on its both ends a first connector for plugging in a discharge tube connector and a second connector for plugging in a transformer circuit output connector, and in the middle a correction capacitor for correcting the parasitic capacity of the discharge tube.
2. Related Art
The transformer for driving discharge tubes such as the cold cathode florescent lamp, hot cathode florescent lamp, mercury lamp, sodium lamp, metal halide lamp, neon lamp, etc has been issued the R.O.C. patent with the U.S. Pat. No. 334,666. The main action of this invention is to have the best working resonance frequency between the ionized inductance on both sides of the AC inverter transformer of the discharge tube and the cold cathode tube of the backlit panel. Therefore, even though the voltage raising transformer is minimized to increase the driving frequency, the luminosity of the discharge tube will not get lowered. However, this type of transformer circuit for the AC inverter has a big defect; that is, it has to be designed case by case according to the individual liquid crystal display, thus the price of the product is relatively high.
Please refer to FIG. 1, which is an explosion view of the local structure of a conventional liquid crystal display. As shown in the figure, the liquid crystal display is composed of a liquid crystal panel 1 and a backlit panel 2. The light source is provided by a discharge tube, such as a cold cathode tube, positioned by the side of the backlit panel 2. To enhance the utility efficiency of the light, a thermal conducting reflection panel 4 similar to a silver plated pet film is provided on the outer side of the discharge tube 3. Conventional technology of connecting the discharge tube 3 with the transformer circuit of the AC inverter is to directly connect the connector 31 of the discharge tube 3 to the output connector of the transformer circuit.
When a liquid crystal display is used, the discharge tube 3 (taking a cold cathode tube as an example) is lit up to make the backlit panel 2 reflect light. The gas inside the cold cathode tube is ionized into ions and lights up the cold cathode tube. The backlit panel 2 is thus reflecting light therefrom. Since ions are good conductors of electricity, they and the cold cathode tube glass form a capacitor in the reflection panel 4 (silver film) with the air as the dielectric. This is called the parasitic capacitor. The value of the parasitic capacity varies with the material combination of the backlit panel 2 and the reflection panel 4. Although the transformer circuit of the cold cathode tube uses a voltage raising transformer, yet the inductance magnitude of this transformer and the parasitic capacity when the lamp is on have a very larger impact on the whole efficiency of the AC inverter working under assigned frequencies.
In general, the parasitic capacity is influenced by the following factors:
1. When the assembly method of the backlit panel 2 is different, the parasitic capacity surrounding the discharge tube 3 (cold cathode tube) in the liquid crystal display will generate different effects according to different liquid crystal displays. PA1 2. The parasitic capacity is also different for different sizes of the liquid crystal display. PA1 3. The value of the parasitic capacity also differs for different types of the discharge tube 3 (cold cathode tube) used in the liquid crystal display.
From the above factors that affect the parasitic capacity, even the liquid crystal displays of the same size will have different states of the surrounding parasitic capacity for the discharge tube 3 of the liquid crystal displays according to different manufacturers and series products. This result will make the retailers obtain the liquid crystal displays via multiple ways because of unstable liquid crystal display supply. The transformer circuit has to fit various liquid crystal display designs. Therefore, not only is the cost increased, the price of the transformer circuit is also getting higher.
In view of the foregoing fact that the parasitic capacity changes under various influences, this will in turn result in the defect that the assembly of the transformer circuit of the AC inverter and the best working frequency of the discharge tube 3 has to fit individual liquid crystal display design. This indeed influences the manufacturing cost of the transformer circuit of the AC inverter and increases the price. The inventor then made every effort in research and, with accumulated experience in the industry, came up with a converter for correcting the resonance frequency between the discharge tube of a liquid crystal display and the transformer of an AC inverter. The convert has on its both ends a first connector for plugging in a discharge tube connector and a second connector for plugging in a transformer circuit output connector of an AC inverter. In the middle, a parasitic capacitor correction apparatus connects both connectors to correct the parasitic capacity of the discharge tube. Therefore, a single AC inverter can be applied to a liquid crystal display of any brand without employing any special transformer circuit for the AC inverter. The price of it can be lowered by mass production.